1. Field of the Invention
The present invention relates to a process for the elimination of toxic effluents in gas phase by the combination of a thermal and photocatalytical process.
2. Description of the Background
High temperature thermodestruction processes and, more rarely, technologies based on ultraviolet radiation, with or without catalysts, and plasma processes are used for the separation of gas or gas-transportable polluting agents.
The property of TiO.sub.2 of catalysing, by means of UV reaction, the oxidation of organic compounds, has been used in numerous applications, in liquid phase and in gas phase. Literature in this respect describes a non-specific oxidative process. Research interest however is concentrated towards groups of hydrocarbons and halogenated compounds, owing to the great importance the diffusion of these compounds has for the health of man and the environment. In processes in gaseous phase the catalyst is both immobilised on the carrier and fluidized by the gaseous stream. This technology however has limits as in most cases the degrading effect on the pollutants, in particular chlorinated pollutants, does not reach mineralization, but stops at intermediates, sometimes toxic, of the starting product.
For the elimination of toxic organic compounds, of the polychlorinated type and dioxins, the association of a thermal process at 600-800.degree. C. with a photochemical process, by means of radiation from 185 to 290 nm, has been proposed (U.S. Pat. No. 5,417,825). It has now been surprisingly found that, by operating under blander conditions with respect to both temperature and radiation, substances in gaseous phase can be effectively degraded by the association of thermal energy and photochemical energy in the presence of a suitable catalyst.